Blended Cement

7/29/2019 Blended Cement

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BLENDED CEMENTIN

Quality construction

UDAI KAFLAYPENDEN CEMENT AUTH ORITY LTD.

QUALITY OF CONCRETEFRESH CONCRETE

Workability

HARDENED CONCRETE

Mechanical Strength

Durability

The only parameter that can be measured with reasonable easeand speed is the Compressive Strength or the MechanicalStrength.

Thus, Concrete is commercially classified according to itsCompressive Strength, like M-5, M-10, M-15, M-20, etc.


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QULAITY CONTROLOF

RAW MATERIALSIN

CONCRETE PRODUCTION

1 . 0 C E M E N T SPENDEN ORDINARY 1981

(33 Grade OPC)Portland Pozzolana Cement 1985(Calcined Clay based)(For CHPC)PENDEN SUPREME 1996(43 Grade OPC)PENDEN SPECIAL 1 99 9

(For THPA)(Portland Slag Ceme nt)PENDEN PREMIU M (Flyash Based) 2005(Portland Pozzolana Ceme nt)


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185

125

Parameters

200

142

2.565.1Sieve Analysis(% > 90 m)

52.054.549.046.028 Days (MPa)

37.0

25.5

0.08

0.85

3.10

357.8

PENDEN

SPECIAL

36.537.835.77 Days (Mpa)

28.928.226.03 Days (MPa)

0.090.140.17Autoclave (%)

1.101.11.5Le-Chatelier

(mm)

188168Final (minutes)

137114

7.4

Initial (minutes)

387.0346.6310.0Blaines (m2/kg)

PENDEN

PREMIUM

PENDEN

SUPREME

PENDEN

ORDINARY

PHYSICAL PROPERTIES COMPARISION

330 330 330

430

530490

535 520

220 220 220

330370 373 368 365

160 160 160220 270 282

255 270

100

150200250

300350

400450500

550

COMPRESSIVE

STRENGTH(kg/cm2)

3Day

7Day

28D

ay

CEMENT TYPE

DUR

ATIO

(D

ays)

3 Day 160 160 160 220 270 282 255 270

7 Day 220 220 220 330 370 373 368 365

28 Day 330 330 330 430 530 490 535 520

IS 269 IS 455 IS 1498 IS 8112 IS 12269 OPC PSC PPC

COMPARISION OF PENDEN CEMENT PRODUCTS

WITH INDIAN STANDARDS REQUIRMENTS


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2.0 AGGREGATESSince aggregates occupy three-quarters of the volume ofConcrete, the properties of aggregates have a major influenceon the properties of concrete.

2 .1 Prope rt ie s o f A ggre ga te sSieve Analysis,Specific Gravity,Moisture Content,Moisture Absorption,

Dry-rodded unit weights.Chemical Reactivity,Soundness,Resistance to Abrasions

2 .2 Aggre ga t e s Q ua lit y2.2.1 Sizes

2.2.2 Particle Shape

2.2.4 Texture

2.2.5 Strength & Abrasions

2.2.6 Resistance to Freezing and Thawing(critically saturated)

(porosity, adsorption and pore structure insufficient unfilled))

2.2.7 Moisture Content, Absorption & Wetting & Drying

2.2.8 Impurities


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A g g r e g a t e s . . .Moisture Content & Absorption

Lightweight Aggregate can absorb 5 29% by weight of dry Aggregate.Normalweight Aggregate absorbs LESS than 2%

Impurities

Clay swells and shrinks on wetting & drying.(3% in fines, 3-10% in coarse aggregates)

Excessive quantities of silt and fine dust increase water requirement.

ORGANIC SUBSTANCE can inhibit the hydration process thereby

delaying setting time and reducing strength.

CHLORIDES, SULPHATES and REACTIVE SILICA should beminimum.

3 .0 M I X I N G W A T E R

Water that is fit to drink is generally regarded as acceptablefor use in mixing concrete.

Water containing one thousand ppm of normally foundminerals acids can be tolerated.

BUT even small amount of various sugars and sugarderivatives should not be used.


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4 .0 ADM IX TU RESChemical Admixtures for Concrete are used for improving variousproperties of Concrete by effect of its surface activity.

3.1 Accelerat ing3.2 Retarding3 .3 Wa te r Re duc ing,3 .4 Air-e nt ert aining.Dosages Solid / Powder

Maximum - 50 g/kg. of cementMinimum - 2 g/kg. of cement

Liquid - 3 litres / m3 of ConcreteSmaller quantities are allowed only if

they are dispersed in part of the mixing water.

QUALITY CONTROLDURING

PRODUCTIONPLACEMENT

AND

POST PRODUCTIONOF CONCRETE


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WORKABILITYCONCRETE can be placed in the formwork and compacted

with minimum effort, without Segregation & Bleeding

CHARACTERESTICSSTABILITY : Should be stable and not segregate during

transportation and placing.MOBIL ITY & : Cohesive and mobile for placing in thePLACEABILITY form, around the reinforcement and should be

able to cast into required shape.COMPACTABILITY : Amenable to proper and thorough

Compaction.FINISHIBILITY : Possible to obtain satisfactory finish.

Fact ors Affect ing WorkabilityConcerning Mix Not Concerning MixWater Cement Ratio Mixing Condition

Type of Cement TemperatureC3A content Time(Workability Loss)FinenessGypsum contentAlkali content

Type of AggregatesMaximum Size

GradingFine Particle Content

Cement Aggregate RatioMineral AdditionsAdmixtures

Water Reducing AgentsAir Entrained Agents


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FACTORS EFFECTING WORKABILITY

Concerning MixFor Better Workability Minimise Particle Interference

Total Specific AreaVoids Content

Aggregate Size (Larger Better)Aggregate ShapeAggregate TextureFine & Coarse Aggregate Mix

Use of Fine sand increases Water Demand, orFor Same Water Content, Workability Decreases.

Water Cement Ratio : Cement paste around aggregatesFill the voids

Workability increases with Water Content.

FACTORS EFFECTING WORKABILITYNot Concerning Mix

TIMEFresh Concrete looses Workability with Time mainly because ofLoss of Moisture : Absorption by aggregates,

Evaporation LossesConsumption in Chemical Reaction

(Reduce from 12 mm to 5 mm in an hour)

TEMPERATUREIncrease in Temperature, Decreases Workability

The Choice of Workability depends upon

Type of Compacting EquipmentSize of the SectionConcentration of Reinforcement


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SEG R EG A TIO NIt is the ability of the concrete mix to separate various constituentsowing to the size and specific weight difference of the particles.

Internal Segregation - Within framework or moldExternal Segregation During transportation or improper handling.

Remedial Measure :Avoid the followings:

Maximum aggregate size above 25 mm,Increase of coarse aggregate fraction,Use of aggregate with improper grading,Use of equal specific weights of aggregates,

(Coarse and Fine Aggregate)Use of flat or elongated aggregates,Decrease in cement content,

Too high or too low Water Cement Ratio.

B LEED IN GBleeding is HIGHER for HIGHER Workability ,

HIGHER Water Cement Ratio,LOWER Cement content.

Water reducing admixtures containingfinely divided mineral additions REDUCE Bleedingligno-sulphatesREDUCESbleeding ratehydrocarboxylicINCREASESbleeding rate

accelerating water reducing agents DO NOTENHANCE bleeding

Silica fume REDUCE bleeding rate but has CRACKINGRISK.


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Excessive Bleeding IMPAIRS

STRENGTH

DURABILITY

Excessive Bleeding RESULTS in

Non-uniformity of Strength

Increased Transverse Permeability

Plastic Settlement Cracking

Poor Bonding between cement matrix and underlying

coarse aggregate & reinforcement

Bleeding is beneficial in hot and windy weather.

If Evaporation exceeds the Bleeding Rate, Plastic Cracks

develop.

Bleeding Effect s

COMPRESSIV E STRENGTH

It can be measured easily and is often taken as an index of theOVERALL Quality wherein many of the desired properties arerelated

Shear Strength

Tensile Strength

Modulus of Elasticity

BondImpact

Abrasion Resistance

Durability


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FACTORS AFFECTING COMPRESSIVE STRENGTH

Water Cement RatioLowering Water/Cement Ratio Increases Strength

Characteristics of CementCharacteristics of AggregatesProportion of Aggregates

Increasing Aggregate/Cement Ratio Increases Strength

The Degree of CompactionIncrease in Compressive Strength by Lowering Water/Cement Ratio may

be restricted if compaction is insufficient.

Efficiency of CuringThe Temperature during CuringThe age of ConcreteCondition of Test

WATER CEMENT RATIOIt governs the quality of the hardened Portland Cement

binder. Strength and Impermeability properties of Concrete

are improved by LOWERING the Water Cement Ratio.

Firstly, in general, to obtain a workable mix, people use more

water than is actually necessary for chemical combination

with the cement. This water occupies space and when it

dries out later, it leaves behind air voids

Secondly, there is decrease in the absolute volume of the

cement paste when dried and hardened.


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300.00

310.00

320.00

330.00

340.00

C

OMP

RESS

IVE

STRE

NGTH(Kg/cm2)

WATER CEMENT RATIO (%)

0.35 0.40

COMPRESSIVE STRENGTH AS A FUN CTION OFWATER CEMENT RATI O

337

313

AGGREGATESThe MORE ANGULAR the sand, the GREATER will

be the WATER REQUIREMENT to produce a given

consistency,

The HIGHER the percentage of voids in a given

sand, the LOWER will be the COMPRESSIVE

STRENGTH ,

The detrimental effects of FREEZING and THAWING

are greatly reduced when the stone sand is

processed to have LESS VOIDS and thereby require

LESS water.


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COMPACTIONThe compactness of Hardened Concrete has a

considerable influence on its fundamental properties,

such as Strength, Impermeabilty and Durability.

Compaction Reduces inter-particle friction

Eliminates air pockets

Presence of 5% voidsDECREASES

Compressive Strength by about 35%

CURINGCuring is the process of maintaining a satisfactory moisture content

in a favourable temperature in concrete during the hydration of the

cementitious materials so that the desired properties of the concrete

are developed.

FUNCTIONS OF CURING

To Prevent Loss of water from Evaporation

Supplement Water consumed in Hydration Process

Curing is essential in the production of quality concrete.

The potential strength and durability of the concrete will be fully

developed if it is properly cured for an adequate period.

Loss of moisture at this stage results in Drying, Shrinkage and

Development of Cracks.


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CURINGOne year Strength of continuously Moist Cured concrete isabout 50 % HIGHER than that of 28 Day Moist Curedconcrete.

No Moist Curing can lower the Strength by about 30%

Moist Curing for first 7 to 14 day may result in CompressiveStrength being 85 to 92% of that of 28 days Moist Curing

Minimum Curing Time 7 Days Moist Curing (IS 456)10 days for hot weather (IS 7861-I)

WATER TEMPERATU REHigher Water temperature cause HIGHER concrete

temperature, as the concrete temperature increases the

water demand increases and STRENGTH decreases for

the same consistency.

Mixing water has the greater effect per unit of weigh of

any of the ingredients on the temperature as its specific

heat is 4 5 times higher that cement and aggregates.


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CONCRETE T EMPERATUREConcrete maintained at Higher temperature during

setting and early hardening has LOWER STRENGTH at

later ages.

Avoiding High Concrete temperature during Curing

REDUCE random Cracking

RESULTS GREATER Strength at Later ages.

STREAM CURIN GTo Develop HIGH Early Strength for early removal of

formwork specially for Precast Concrete.

CONCRETE TEMPERATUREThe rate of reaction between cement and water varies with

temperature. It proceeds slowly at low temperature down to -

12 C and rapidly at high temperature somewhat below the

boiling point of water.

Below 10 C are unfavourable for the development of Early

Strength

Below 5 C the development of early Strength is greatly retarded

At freezing temperature, little strength develops

Curing at temperature in excess of 70 C is not as beneficial as

prolonged curing at lower temperature.

Autoclaving at temperature above 160 C may produce strength

in few hours equal to 28 days of curing at 20 C.


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DURABILITY. . . ability of concrete to RESIST weathering action,chemical attack, abrasion and other conditions of service.

DURABLE CONCRETE will RETAIN its ORIGINAL FORM ,QUALITY and SERVICEABILITY when exposed toEnvironment.

DURABILITY is a function of

The Choice of Cement and its dosageThe Choice of Aggregates (form, cleanliness, stability, etc.)

The Water (quality, content and water-cement ratio)The use of appropriate AdmixturesThe batching and casting methodsThe curing of Concrete

Of late, the focus of construction has been shifted from

STRENGTH to DURABILITY

High Strength cements have played havoc in building sector.

These resulted in Development of Shrinkage Cracks,

Vulnerability to Severe Environment,

Reduced Life of the Structure.

Durability . . .

DURABILITY of Concrete is impaired due to:

Inability of achieving compaction leading tohoney combing

Corrosion of reinforcements due to chloride diffusion andcarbonation of concrete, cracking of concrete,

Volume changes due to sulphate attack, shrinkage,alkali silica reaction, cracking of concrete, etc.


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DURABILITY & CONCRETE FAILURES

(Causes)

EXTERNAL

WeatheringAttack by Natural / Industrial liquids,Bacterial Growth

INTERNAL

Alkali Aggregate ReactionVolume Change due to non-compatibility of Thermal &

Mechanical properties of Aggregates & Cement paste.Presence of SulphatesPresence of ChloridesIngress of Moisture / Air

RECOMMENDATION FOR DURABLE

CONCRETE

Limits for Maximum Water-Cement Ratio

Minimum Cement Content

Cover Thickness

Type of Cement

Chloride Content in Concrete

Sulphate Content in Concrete

CONSIDERATIONSSituation of Placing

Congestion of Reinforcement

Cover Thickness

Workability of Concrete

Characteristics of aggregates


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HONEYCOMBIt occurs when the mortar does not fill the space between the

coarse aggregates. Its presence indicates that first stage of

consolidation has not been completed.

CAUSES - Use of improper or faulty vibrators,Poor vibrations procedures,

Unsystematic insertion of mortar at haphazard

angles,

Insufficient paste to fill the voids,

Improper ratio of sand to total aggregate,

Poor aggregate grading,Improper workability,

Insufficient clearance between the reinforcement

bars.

Entrapped Air VoidsThe amount of entrapped air in concrete is depended upon:

Vibratory equipment,

Vibration Procedures,

Properties of concrete mix,

Location in the placement.

To reduce air voids, the distance between internal vibratorinsertions should be reduced and the time at each insertion

increased.


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Pour LineThese are dark lines showing on the formed surface

demarking the boundary between adjacent batches of

concrete. They indicate that when vibrating a layer, the

vibrator was not lowered far enough to penetrate the

layer below.

SAND STREAKIN GCAUSES - Heavy bleeding along the form,

Character of the materials,

Proportions of the materials,

Method of depositing concrete,

Harsh and wet mix with

Less Cement and More Water,

Poorly Graded Aggregate,

Dropping concrete mix through

reinforcing steel,Using Thick Lifts without

adequate Compaction,

Vibrators attached to leaking form.


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DENSE & IMPERMEABLE CONCRETE MASS

MORE DURABLE

Resistance to Sulphate Attack

Resistance to Acid AttackResistance to Chloride IngressionCarbonation ShrinkageAlkali Silica Reaction (ASR)

Permeability of Cement Paste INCREASES exponentially withINCREASE in Water-Cement ratio above 0.45.

Cement Content

Ensure sufficient alkalinity to provide Passive EnvironmentTo overfill the voids between the aggregates

REDUCED PERMEABILITY RESULTS I N HIGH RESISTANCE TO SULFATE ATTACK

HIGH RESISTANCE TO CHLORIDE INGRESSION

MINIMISING THE RISK OF ALK ALISIL ICA REACTION

HIGH RESISTANCE TO ACIDS AND CHEMICALS(REDUCED LEACHING)

RESISTANCE TO CARBONAGE SHRINKAGE

DURABILITY


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Sulphate Atta ck

Sulphate attack causes expansion, loss of strength and eventually

transform the materials into musky mass. The rate and depth of

sulphate attach depends upon the characteristics of concrete

strength, porosity, permeability and chemical composition of

hardened cement paste.

Combination of sulphate with Calcium ion liberated during

hydration of cement to form gypsum,

Combination of sulphate ion, gypsum and hydrate Calcium

Aluminate to form Calcium Sulfo-aluminate hydrate (ettringite),

Both these chemical reactions result in increase in solid volume.The formation ofettringiteis the cause of most of the expansion anddisruption of concrete by sulphate solution.

Chloride Att ack

Chloride can harmfully affect the durability of both

concrete and reinforcement.

The chloride ion content of concrete must be kept lower

and the ionic penetration from outside must be prevented

or hindered.

Chloride dissolved in water increases the rate of leaching

of portlandite thus increasing the porosity or mortar and

concrete. As a result of the attack, the concrete swells,

losses stiffness and strength and becomes more sensitive

to other environmental attacks (sulphate, frost, etc.)

Chloride attack will result in the corrosion of the concrete

reinforcement. Chloride attack can take place if oxygen

and moisture are present.


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Diffusion of Chloride Ions at 25C in Cement Paste ofWater to Cement ratio 0.5

Type of Cement Diffusivity(x10-9 cm2/sec)

Sulphate Resistance Portland Cement (SRPC) 100.00

Ordinary Portland Cement (OPC) 44.70

Portland Pozzolana Cement (PPC) 14.70(70% OPC 30% Flyash)

Portland Slag Cement (PSC) 4.10(35% OPC, 65% Slag)

The rate and depth of Chloride penetration into concrete depend uponthe permeability of concrete. It can be decreased by

Decreasing the water/cement ratioIncreasing the cement contentIncreasing the length of curing

Acid AttackThe deterioration of Concrete by acids is primarily the result ofreaction between these chemicals and Calcium Hydroxide of thehydrated Portland Cement. In most cases, the chemicalreaction results in the formation of water soluble calciumcompounds which are then LEACHED away by aqueoussolutions.

A Dense Concrete with Low Water Cement Ratioprovides an acceptable degree of protection againstAcid Attack.


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Carbonation Shrinkage

When concrete is exposed to carbon dioxide, a reaction

producing carbonates takes place which is accompanied byshrinkage. The source of carbon dioxide can be either theatmosphere or water carrying dissolved carbon dioxide.

CarbonationEffect of Carbon Dioxide

Carbon dioxide contained in the air is potentiallydangerous for concrete durability because it can attack allof the hydrates in the hardened cement. This alarmingprospective concerns only low strength porous concrete.

Alka li Silica Reac tionAlthough aggregates is commonly considered to be inertfiller in concrete, some aggregates may react with alkalispresent in the pore fluids of concrete. Under such adverseconditions and in presence of moisture, this may lead toexpansion and subsequent cracking of the Concrete.

A Dense Concrete with Low permeability and LowWater Cement ratio provides Resistance againstAlkali Silica Reaction.


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5Cs OF DURABLE CONCRETECONSTITUENT MATERIALS

COVER

COMPACTION

CURING

CARE

293

318 320

379368

335352 345

278 278271

310 300

268287

261

218 216 220

260229 227 231 227

200

250

300

350

400

COMPRESSIVE

STRENGTH

(kg/cm

2)

3Day

7Day

28Da

y

CEMENT TYPE

DURATION

(Days)

3 Day 218 216 220 260 229 227 231 227

7 Day 278 278 271 310 300 268 287 261

28 Day 293 318 320 379 368 335 352 345

OPC PPC PSC OPC:PPC

OPC:PSC

PSC:PPC

OPC:PPC:PSC

OPC:PPC:PSC(M

COMPRESSIVE STRENGTH OF M20

CEMENT CONCRETE CUBES

PCAL Laboratory Result


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0.00

5.00

10.00

15.00

20.00

25.00

30.00

STR

EN

G

TH

(M

Pa

3 Day 7 Day 28 Day

DURATION (DAYS)

M 20 CIVIL CONCRETE CUBE TESTS

PSC PPC OPC

M30 CIVIL CONCRETE CUBE TESTS

32.80

37.80 4

6.80

35.40 4

2.50

45.86

44.50

37.30

30.70

0.00

10.00

20.00

30.00

40.00

50.00

3 Day 7 Day 28 Day

DURATION (DAYS)

ST

RENGTH

(MPa)

PSC PPC OPC


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M 40 CIVIL CONCRETE CUBE TESTS

27.77

36.97

42.37

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

3 Day 7 Day 28 Day

DURATION (DAYS)

STRENGTH(

MPa)

TASHI DELEK

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Blended Cement